122

XML Overview

   Implementing XML Based Applications  on page 164 Provides guidelines 

for developers on how best to implement XML based applications. This sec 

tion includes an in depth discussion of the various XML processing technolo 

gies that developers can use to implement their applications. It covers the 

advantages and disadvantages of the principal XML programming models and 

provides recommendations for when you should consider using each of the 

models.

   Performance Considerations  on page 182 Outlines guidelines for maxi 

mizing performance. This section makes specific recommendations for ap 

proaches developers can take to keep performance at an acceptable level.

Many of these concepts for designing XML based applications are generic in

nature; they apply to any application handling XML documents. Since Web ser 

vices are XML based applications, these concepts especially apply to the design

of Web service endpoints and clients. The chapter emphasizes the design consid 

erations that should be kept in mind when developing Web service endpoints and

clients. 

Although it presents the basic XML concepts, this chapter assumes that you

have a working knowledge of the XML processing technologies, especially SAX,

DOM, XSLT, and JAXB. (Refer to Chapter 2 for more details on these technolo 

gies.) Whenever possible, the chapter uses the scenarios introduced in Chapter 1

to illustrate various points.

4.1

XML Overview

While you may already be familiar with XML, it is important to understand XML

concepts from the point of view of applications handling XML documents. With

this knowledge, you are in a better position to judge the impact of your design deci 

sions on the implementation and performance of your XML based applications.

Essentially, XML is a markup language that enables hierarchical data content

extrapolated from programming language data structures to be represented as a

marked up text document. As a markup language, XML uses tags to mark pieces

of data. Each tag attempts to assign meaning to the data associated with it; that is,

transform the data into information. If you know SGML (Standard Generalized

Markup Language) and HTML (HyperText Markup Language), then XML will

look familiar to you. XML is derived from SGML and also bears some resem 

blance to HTML, which is also a subset of SGML. But unlike HTML, XML